1. Field of the Invention
The present invention relates to a control apparatus for an internal combustion engine capable of limiting the target opening degree of an electronic throttle valve so as to prevent the running speed (vehicle speed) from exceeding a permitted maximum speed.
2. Description of the Related Art
In a known control apparatus for an internal combustion engine, when the speed of a vehicle with a control apparatus mounted thereon reaches a permitted maximum speed, the throttle opening or the opening of a throttle valve is controlled in such a manner that if the actual vehicle speed is increasing during the time when the throttle opening is being driven to open or increase, the throttle opening is controlled to close or decrease, whereas if the actual vehicle speed is not increasing, the throttle opening is maintained as it is, whereby the vehicle speed is prevented from exceeding the permitted maximum speed (for example, see a first patent document: Japanese patent application laid-open No. 61-277843).
However, as is well known from the characteristic between the throttle opening and the amount of intake air, there exist a first range in which the amount of air increases linearly in accordance with the increasing throttle opening and a second range in which the amount of intake air remains substantially unchanged with respect to a change in the throttle opening.
Accordingly, in case where the actual vehicle speed is increasing with the throttle opening being in the second range at the time when the vehicle speed reaches the permitted maximum speed while the throttle opening is being driven to open or increase, the actual amount of intake air sucked into the engine will not decrease even if the throttle opening is driven to close or decrease as long as the throttle opening is in the second range.
As described above, in the known control apparatus for an internal combustion engine, the actual amount of intake air is not sometimes decreased even if the throttle opening is driven to close or decrease. Therefore, a problem arises that there is a possibility of the vehicle speed exceeding the permitted maximum speed to a substantial extent.
In addition, in order to prevent the vehicle speed from exceeding the permitted maximum speed, it is often necessary to acquire a signal indicative of the value of the actual vehicle speed, and hence another problem arises that if such a vehicle speed signal is missed due to an operation defect, a technical defect or the like, an overspeed preventive function will become unable to operate properly, as a result of which the permitted maximum speed might be exceeded.